1. Field of the Invention
The invention relates generally to a lifting platform for double-tracked vehicles, such as motor vehicles, and more particularly to such an apparatus having two horizontal vehicle supports including support elements for the vehicle wheels, and an axis elevator shiftable on longitudinal rails between the two vehicle supports.
2. Discussion of Related Art
Lifting platforms for motor vehicles of the accordion or jack type including a so-called axis elevator for lifting a vehicle axis are known. This axis elevator is a separate lifting device extending transversely to the two longitudinal supports and having a base capable of providing support and including pairs of traveling rolls disposed at the end sides thereof On this base, hydraulically operable lifting cross-bars are mounted, the upper telescopic bar of which is provided with two longitudinally adjustable support elements for the respective vehicle axis. The axis elevator can be manually moved under the respective vehicle axis by means of its pairs of traveling rolls running on inner longitudinal rails of the vehicle supports. By extending the thus positioned axis elevator, the respective vehicle axis is lifted by a predetermined amount so that the associated wheels are relieved and certain tests, for example, tests concerning the free motion of the axis, may be carried out.
In a number of applications, continuous footings having a relatively narrow central pit for receiving the hydraulic jacks and a box containing their drive units as well as two recesses extending in the longitudinal direction of the vehicle supports have proved to be particularly advantageous for lifting platforms of the jack-type. To cover the recesses on the floor level when the vehicle supports are in a lifted state and to thus generate an essentially continuous floor surface, a means referred to as floor compensation is provided which consists of a plate member capable of providing support and disposed in the respective recess to be liftable and lowerable, for example, by means of pressure fluid cushions, respectively. The pressure cushions are preferably filled with pressurized air in synchronism with a movement of the vehicle supports so that the plate members are lifted to their upper position on the floor level. As yet, however, it has been thought to be impossible to provide such jack-type lifting platforms accommodated in a continuous footing with an axis elevator.
From German utility model 7 332 957 a cover means for the foundation pits of hydraulic lifting platforms for motor vehicles is known wherein a small lifting cylinder, the piston of which carries a cover plate provided with a recess for the lifting platform jack, is associated with the lifting platform cylinder. When the lifting platform is extended, this closing plate is lifted to the floor level by the lifting piston and is fixed there. When the lifting platform is retracted, the closing plate is positioned under the support of the lifting platform. Additionally, a cover plate is provided which is taken along by the support of the lifting platform when the lifting platform is extended and which covers the foundation pit when the lifting platform is in its retracted state. This cover is only suitable for a specially designed lifting platform and poses relatively high technical requirements, particularly due to the two different cover elements as well as due to the additional pressure cylinder.
Further, from German patent publication 197 04 760 a drive-on lifting platform for motor vehicles is known, the lifting table of which is provided with rails for the reception of an additional transportation means for the wheels of the motor vehicle in the area of the two vehicle axes, these rails being mounted on the lifting table forming a pair transverse to the vehicle axis.
Additionally, from French patent 2 341 515 a drive-on lifting platform is known which comprises longitudinal rails which form the supports for the wheels of the vehicle to be lifted and are liftable and lowerable along a single vertical column. For additionally lifting the vehicle for the purpose of relieving the wheels of the vehicle, a lifting means capable of being lifted and lowered with the aid of pressure cushions is provided between the two longitudinal rails, the projecting support arms of which lifting means can be positioned under the axes of the vehicle to lift the vehicle from the two rails.